W32.Navidad is a mass-mailing worm program. Using MAPI, the worm replies to all inbox messages that contain a single attachment. This worm is able to distribute itself through any MAPI-compliant email client, including Microsoft Outlook. However, email messages that are infected with this worm can be received by any email client. The worm utilizes the existing email subject line and body and attaches itself as Navidad.exe. Due to the bugs in the code, when the worm is executed, it causes your system to be unusable.

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Technical Description

NOTE:
If you are running Windows 95 or Windows 98, it is assumed that Windows is located in C:\Windows. If you are running Windows NT or Windows 2000, it is assumed that Windows is located in C:\Winnt. If Windows is installed in a different directory, make the appropriate substitutions.

This is how the worm works:

When executed, the worm displays a dialog box with the cryptic letters

UI

and the title

Error

If you are running Windows 95 or Windows 98, the worm adds the following registry key:

HKEY_USERS\.DEFAULT\Software\Navidad

If you are running Windows NT or Windows 2000, the worm adds the following registry key:

HKEY_CURRENT_USER\Software\Navidad

This key was supposed to be used to see if the computer was already infected. However, due to bugs in the code, the registry key is not used.

If you are running Windows 95 or Windows 98, the worm adds the following registry key:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

with the value

Win32BaseServiceMOD=\Windows\System\Winsvrc.exe

If you are running Windows NT or Windows 2000, the worm adds the following registry key:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

with the value

Win32BaseServiceMOD=\Winnt\System32\Winsvrc.exe

The worm copies itself into the Windows system folder as Winsvrc.vxd. Due to the difference in file name, the virus does not execute properly at startup. After the file has been copied, the worm modifies two additional registry keys. If you are running Windows 95 or Windows 98, the worm changes

Due to the mistake in the file name, the system is unusable. Whenever an .exe file is executed, the Windows prompts you for the location of Winsvrc.exe. The net result is that no program files can be launched. This may cause system instability and you may have difficulty restarting the system.

Next, the worm begins the email routine. The worm uses MAPI to send mail and works with any MAPI-compliant email client, including Microsoft Outlook. The worm checks for all messages in your Inbox and replies to those messages that have one attachment. The reply consists of the same subject line and body, but contains the worm attached as NAVIDAD.EXE.

Finally, the worm places a blue eye icon in the system tray of the taskbar. When the mouse pointer is over the icon, the worm displays a yellow dialog box that states

Lo estamos mirando... (In English: We are watching it...)

When you click the icon, a dialog box with a button appears. The button contains the following text:

If you close the dialog box by clicking the X instead of clicking the button, the following message appears:

buena eleccion (In English: Good selection)

and exits. Despite the warning of losing the computer, no further changes are made to the system.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.

Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.

Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.

Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.

Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.

Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.

If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.

Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.

Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.

Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.

Removal

The Symantec AntiVirus Research Center (SARC) has developed a tool to help you repair the damage done by the worm. The W32.Navidad Fix Tool, and instructions on how to use it, are available here
.

If you prefer to remove the worm without using the tool, or if the tool does not work on your computer, then follow the instructions in each section in the order shown. We strongly recommend that you read and understand the entire procedure before proceeding.

To remove this worm, you must do the following:

Copy Regedit.exe to Regedit.com (in some cases).

Edit the registry, and remove keys and changes made by the worm.

Set Windows to show all files.

Delete files placed on the computer by the worm.

Run a full system scan.

To copy Regedit.exe to Regedit.com:
If you cannot start program files, or if you see the message "Windows cannot find winsvrc.exe," then you'll need to copy Regedit.exe to Regedit.com.

Do one of the following, depending on which operating system you have installed:

Windows 95/98. Click Start, point to Programs, and then click MS-DOS Prompt.

Windows Me. Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt.

Windows 2000.

Click Start, and click Run.

Click Browse, and then browse to the \Winnt\System32 folder.

Double-click the Command.com file, and then click OK.

Type cd \winnt and then press Enter.

Type copy regedit.exeregedit.com and then press Enter.

Type start regedit.com and then press Enter.

Proceed to the section "To edit the registry and remove keys and changes made by the worm."

NOTE: This will open the Registry Editor in front of the DOS window. After you finish editing the registry and have closed the Registry Editor, close the DOS window as well.

To edit the registry and remove keys and changes made by the worm:
Follow these steps to undo the changes made to the Windows registry:

CAUTION
: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry can result in permanent data loss or corrupted files. Please make sure you modify only the keys specified in this document. For more information about how to back up the registry, please read the document How to back up the Windows registry
before proceeding with the following steps. If you are concerned that you cannot follow these steps correctly, then please do not proceed. Consult a computer technician for more information.

Start the Registry Editor if necessary:

If you have performed the procedure in the previous section, the Registry Editor is already open. Skip to step 4.

If it was not necessary to perform the procedures in the previous section, go on to step 2.

Click Start, and click Run. The Run dialog box appears.

Type regedit and then click OK. The Registry Editor opens.

NOTE: If you see an error message or the Registry Editor does not open, go back to and follow the instructions in the previous section.

Navigate to and delete the following keys:

NOTE: It is likely that you will find only one.

HKEY_CURRENT_USER\Software\Navidad
HKEY_CURRENT_USER\Software\Emanuel

Navigate to and select the following key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

In the right pane, look for and select any of the following values that exist:

NOTE: Some other variants of this have been seen, such as win b service. If in doubt, delete it. Removing items from the \Run key does not actually delete files from the hard disk--it only prevents them from being run when the computer starts.

Press Delete, and then click Yes to confirm.

Navigate to and select the following key:

HKEY_CLASSES_ROOT\exefile\shell\open\command

CAUTION: The HKEY_CLASSES_ROOT key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure you browse all the way along this path until you reach the \command subkey.
Do notmodify the HKEY_CLASSES_ROOT\.exe key. Domodify the HKEY_CLASSES_ROOT\exefile\shell\open\command subkey that is shown in the following figure:

<<=== NOTE: This is the key that you need to modify.

Double-click the (Default) value in the right pane.

Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)

NOTE: The Registry Editor will automatically enclose the value within quotation marks. When you click OK, the (Default) value should look exactly like this: ""%1" %*"

Make sure you completely delete all value data in the command key prior to typing the correct data. If a space is left accidentally at the beginning of the entry, any attempt to run program files will result in the error message, "Windows cannot find .exe." or "Cannot locate C:\ <path and file name>." If this happens to you, start over at the beginning of this document, making sure to completely remove the current value data.

Restart the computer.

To set Windows to show all files:
You need to do this to make sure that you can find the files installed by W32.Navidad.

Start Windows Explorer.

Click the View menu (Windows 95/98) or the Tools menu (Windows Me), and then click Options or Folder Options.

Click the View tab, and uncheck "Hide file extensions for known file types."

Click Show all files, and click OK.

To delete the files left by the worm:
To delete the files installed by W32.Navidad, follow these steps:

Click Start, point to Find or Search, and then click Files or Folders.

Make sure that "Look in" is set to (C:) and that Include subfolders is checked.

In the "Named" or "Search for..." box, type--or copy and paste--the following:

navidad*.exe

Click Find Now or Search Now.

Delete any copies that you find.

Delete the text navidad*.exe from the "Named" or "Search for..." box.

In the "Named" or "Search for..." box, type--or copy and paste--the following:

winsvrc.* winsvic.* wintask.* emanuel*.exe

Click Find Now or Search Now.

Delete any files named Winsvrc.exe, Winsvrc.vxd, Winsvic.vxd, Wintask.exe, Wintask.vxd, or Emanuel.exe that you find.

NOTE: If Norton AntiVirus is installed and running on this computer, you may be alerted that the files are infected when you complete the previous steps. If that happens, choose Delete, and ignore any subsequent Windows messages saying that the file cannot be deleted. (This is Windows alerting you that it cannot find the specified file. It cannot find the file because it has already been deleted by Norton AntiVirus.)

To run a full system scan:
Start Norton AntiVirus (NAV), and make sure the your virus definitions are dated November 9, 2000, or later. If they are not, then run LiveUpdate. Finally, run a full system scan. If you have any version of NAV other than NAV 2001, then make sure that NAV is set to scan all files.